1. Field of the Invention
The present invention relates in general to a method and system for cementing a liner and, in particular, to a system and method for cementing a liner and setting a liner top packer with a mechanical setting tool.
2. Brief Description of Related Art
Oil and gas wells are conventionally drilled with drill pipe to a certain depth, then casing is run and cemented in the well. The operator may then drill the well to a greater depth with drill pipe and cement another string of casing. In this type of system, each string of casing extends to the surface wellhead assembly.
In some well completions, an operator may install a liner rather than an inner string of casing. The liner is made up of joints of pipe in the same manner as casing. Also, the liner is normally cemented into the well. However, the liner does not extend back to the wellhead assembly at the surface. Instead, it is secured by a liner hanger to the last string of casing just above the lower end of the casing. The operator may later install a tie back string of casing that extends from the wellhead downward into engagement with the liner hanger assembly.
When installing a liner, in most cases, the operator drills the well to the desired depth, retrieves the drill string, then assembles and lowers the liner into the well. A liner top packer may also be incorporated with the liner hanger. A cement shoe with a check valve will normally be secured to the lower end of the liner as the liner is made up. When the desired length of liner is reached, the operator attaches a liner hanger to the upper end of the liner, and attaches a running tool to the liner hanger. The operator then runs the liner into the wellbore on a string of drill pipe attached to the running tool. The operator sets the liner hanger and pumps cement through the drill pipe, down the liner, and back up an annulus surrounding the liner. The cement shoe prevents backflow of cement back into the liner. The running tool may dispense a wiper plug following the cement to wipe cement from the interior of the liner at the conclusion of the cement pumping. The operator then sets the liner top packer, if used, releases the running tool from the liner, and retrieves the drill pipe.
A variety of designs exist for liner hangers. Some may be set in response to mechanical movement or manipulation of the drill pipe, including rotation. Others may be set by dropping a ball or dart into the drill string, then applying fluid pressure to the interior of the string after the ball or dart lands on a seat in the running tool. The running tool may be attached to the liner hanger or body of the running tool by threads, shear elements, or by a hydraulically actuated arrangement.
In another method of installing a liner, the operator runs the liner while simultaneously drilling the wellbore. This method is similar to a related technology known as casing drilling. Retrievable bottom hole assemblies are known for casing drilling, but in casing drilling the upper end of the casing is at the rig floor. In typical liner drilling, the upper end of the liner is deep within the well and the liner is suspended on a string of drill pipe. In casing drilling, the bottom hole assembly can be retrieved and rerun by wire line, drill pipe, or by pumping the bottom hole assembly down and back up. With liner drilling, the operator sets a liner hanger, releases a liner hanger running tool, and then retrieves the inner string. The liner can then be cemented using a cement retainer set on the drill pipe and run into the wellbore. A valve in the retainer then closes and holds the cement below the retainer and behind the liner. Unfortunately, this method does not allow for testing of the casing or liner.
A liner top packer is often used to isolate the top of the liner from the wellbore. The liner top packer is set by two drill pipe runs. The first run cleans the liner top, and the second deploys and sets the liner top packer. Unfortunately, this is a time consuming and expensive process due to the additional run requirements needed to first retrieve the bottom hole assembly, then set and cement the liner, and finally to set the liner top packer.
A displacement plug may be used to prevent cement in the annulus between the liner and wellbore or casing from backflowing into the liner during setting of the liner top packer: Conventional methods for setting a liner top packer include use of float shoes and float collars. In these methods, plug failure is not an issue because the float equipment will take over in the event there is a plug failure. However, where the liner is drilled with retrievable equipment, there is no float equipment to backup the displacement plug. Where the displacement plug fails to latch, fluid pressure must be maintained on the cement to prevent backflow. Conventional packer setting tools set the liner top packer by pulling upward on the packer setting tool and releasing any downward force on the liner top packer until dogs in the packer setting tool move into position over a setting sleeve of the liner top packer. Where the displacement plug fails to latch, the process of setting the packer relieves the pressure on the cement allowing it to backflow. In addition, releasing the drill string weight from the liner top packer may cause the liner top packer to move out of position relative to the liner top. Therefore, there is a need for a mechanical liner top packer setting tool that overcomes the cost, time, and reliability problems of prior art methods.